This paper summarizes the results from the successful in-space demonstration of a novel propulsion system using an ADN-based monopropellant. The basic mission for the High Performance Green Propulsion system (HPGP) has been successfully completed and all objectives of TRL 7 have been met. The demonstrations have been performed on "Mango" the main satellite of the two Prisma satellites. Prisma's aim is to perform autonomous formation flying, autonomous rendezvous, homing, proximity operations as well as other technology demonstrations. Mango is equipped with both a hydrazine and the HPGP propulsion system to provide the AV required for the formation flying maneuvers. The AV can be generated separately by the hydrazine or HPGP propulsion systems, or in combined operation. The HPGP propulsion system uses the first ADN-based storable monopropellant (LMP-103S) qualified for space flight, which has demonstrated a 32% higher density impulse than hydrazine in space. LMP-103S is defined as a "Green" propellant due its characteristics (i.e. low toxicity, non-carcinogenic and being environmentally benign). LMP-103S is approved for transport according to UN Class 1.4S and was therefore shipped with the satellites and all ground support equipment as air cargo to the Prisma launch site. Loading the spacecraft with LMP-103S was declared as a "Non-Hazardous Operation" by the Yasny Range Safety Authority and SCAPE operations were not required during fueling. Decontamination and waste handling of the LMP-103S was a simple task thus using LMP-103S significantly reduced lead time, cost and significantly simplified the pre-launch activities compared to Hydrazine. The HPGP in-space demonstrations included commissioning, specific HPGP-only firings and combined operations with the hydrazine system. After one year of operation in space, more than 320 sequences comprising over 34,000 pulses have been fired as continuous, pulse mode or off-modulation firings. Performance mapping has been performed by executing firing sequences with pulse durations from 50ms up to 60 seconds over a range of duty cycles from 0.1% to 99%. Pulse trains lasting up to 90 minutes have been executed. Pulse mode and single pulse 1-bit predictability has been demonstrated to be very accurate for the HPGP system. To date a burn time of more than 23 hours has been accumulated and 50% of the propellant has been consumed. The HPGP thruster thrust and specific impulse measured in-space, by means of onboard sensors, are slightly higher than the measurements performed from near-vacuum tests on ground. Back-to-back performance measurements between the HPGP and Hydrazine propulsion systems show that the average Isp is 8% higher for LMP-103S than compared to Hydrazine when approximately 50% of the propellant has been consumed for both systems. As a result of the successful demonstrations on Prisma, it is concluded that HPGP technology is emerging as a proven technology for improved performance, enhanced volumetric efficiency, reduction of propellant handling hazards and significantly shorter and simplified pre-launch operations. The Prisma mission is ongoing and is planned to be extended for another year, with the HPGP system providing AV for new mission objectives. The HPGP technology has already been selected as the propulsion baseline for new small European and U.S. missions where improved density impulse is of major importance.
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